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2008 Cadillac CTS DI AWD Black Raven
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Discussion Starter #1
I have p225 50 r17's ..... on my stock cadillac rims.... What is the biggest tire size I can go with this rim??? I want to make the rear tires wider.... thanksssss
 

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> BMUU
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there's a formula that Odysseus (sp?) came up w/ ... maybe some other people here know it.

hes the "go to" guy when it comes to wheels/tires.
 

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2014 SRX AWD Platinum Ice/2010 CTS Sedan 3.6 AWD Silver
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644 Posts
I bought 235/45r17 and am hoping they fit (they're still in the basement, damned RSAs are hanging in and refusing to wear out the last bit!). 245/45r17 is actually closer to stock diameter (which is important for speed to be accurate), but I don't think they'll fit up front unless you use spacers to increase the clearance. The extra 10 mm is divided on either side of the wheel, so it means there needs to be about 5mm spare clearance - it's going to be close. Take a look and you'll see what I mean. In case you didn't know, the first number in tire sizing is the tread width, the second is the ratio between tread width and sidewall height, and the last is the wheel diameter.

I asked around the forum and never had confirmation from anyone that 235/45r17 or 245/45r17 would fit on OEM 17" rims and not rub. I decided to go 235 since it has a better chance of working without a spacer.

-GT
 

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2008 Cadillac CTS DI AWD Black Raven
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341 Posts
Discussion Starter #4
hey cool.... I hear I can go to tirerack.com and they can tell you the ratio formula etc..
 

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2003 CTS Manual Trans., '93 STS
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For the rear, the only issue is fitting the wider tire on the rim, as long as you keep the diameter the same. On the fronts, you're limited by the upper A-Arm pinch bolt to a 235 series tire on the stock 51mm offset wheel. The rear wheel wells will accommodate up to a 275 series tire, if the proper offset and associated wheel width are adhered to. On the stock 7.5" wide wheel, 225's are recommended, but I'm willing to bet a 245 will fit just fine (245/45R17) as they're only about 1/3" wider on each side of the wheel.

There are plenty of tire size calculators on-line, and yes, I've posted the actual formula to calculate it yourself, if you wanted.
 

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'04 CTS
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One of the great things about TireRack is that they list two important and hard-to-find pieces of information about any tire they sell. First is the "section width" which tells you how wide the fullest part of that tire is. Second is a listing of what rim widths the tire manufacturer considers acceptable for that specific tire, including the rim width that is used for the section width specification. Formulas are great but it's nice to know what the real deal is for the specific tire you're interested in. Oh, and watch out for inconsistencies, sometimes the person that enters the info makes a typo. You can usually tell by looking at a size above and below the one you're interested in and comparing the numbers.
 

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Sedan de Ville, CTS
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I have p225 50 r17's ..... on my stock cadillac rims.... What is the biggest tire size I can go with this rim??? I want to make the rear tires wider.... thanksssss
245-45-17 per Discount Tire website.

some 18s and 19s too, if you really want to throw money away.
 

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2003 CTS Manual Trans., '93 STS
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You wont' be able to tighten the lug nuts on the front wheels with 245's on, if you're using stock wheels with 51mm offset. 235's will be very close to the upper a-arm pinch bolt. If you want to run 245's you need between 40 and 45mm offset (40 being preferred).
 
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